FIX: deleted misconfigured embeddable hosts (#19833)

When EmbeddableHost is configured for a specific category and that category is deleted, then EmbeddableHost should be deleted as well.

In addition, migration was added to fix existing data.

app/models/category.rb

@@ -130,6 +130,7 @@ class Category < ActiveRecord::Base
 
   has_many :category_required_tag_groups, -> { order(order: :asc) }, dependent: :destroy
   has_many :sidebar_section_links, as: :linkable, dependent: :delete_all
+  has_many :embeddable_hosts, dependent: :destroy
 
   belongs_to :reviewable_by_group, class_name: "Group"
 

db/migrate/20230111223803_delete_misconfigured_embeddable_hosts.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class DeleteMisconfiguredEmbeddableHosts < ActiveRecord::Migration[7.0]
+  def up
+    execute(<<~SQL)
+      DELETE FROM embeddable_hosts eh1
+      WHERE eh1.id IN (
+        SELECT eh2.id FROM embeddable_hosts eh2
+        LEFT JOIN categories ON categories.id = eh2.category_id
+        WHERE eh2.category_id IS NOT NULL
+        AND categories.id IS NULL
+      )
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

spec/models/category_spec.rb

@@ -577,6 +577,12 @@ RSpec.describe Category do
       expect(SiteSetting.shared_drafts_category).to be_blank
     end
 
+    it "deletes related embeddable host" do
+      embeddable_host = Fabricate(:embeddable_host, category: @category)
+      @category.destroy!
+      expect { embeddable_host.reload }.to raise_error(ActiveRecord::RecordNotFound)
+    end
+
     it "triggers a extensibility event" do
       event = DiscourseEvent.track(:category_destroyed) { @category.destroy }